LED lighting is transforming the lighting industry, such that light products are no longer merely on/off devices, but have become sophisticated devices with more elaborate control options, made possible by the easy controllability of LEDs.
The required current to be supplied by a driver circuit varies for different lighting units/modules, and for different configurations of lighting unit. The latest LED driver circuits are designed to have sufficient flexibility that they can be used for a wide range of different lighting units, and for a range of numbers of lighting units. For this purpose, an intelligent electronic driver circuit in a LED lighting fixture (often called “ballast”) is now frequently separate from the lighting module itself, to enable this flexibility in the design of a lighting system.
It is known for the driver circuit to operate within a so-called “operating window”. An operating window defines a relationship between the output voltage and output current that can be delivered by the driver circuit. Providing the requirements of a particular lighting load fall within this operating window, the driver circuit is able to be configured for use with that particular lighting load, giving the desired driver circuit flexibility. This means a driver circuit is able to be used for LED units of different design and from different manufacturers and for a wide range of applications, providing that the required current and voltage setting fits the operating window. It also enables lighting generation upgrades without changing the driver circuit.
The driver circuit needs to have its output current set to the desired level within its operating window. This can be achieved by programming the driver circuit to deliver a specific current.
However, an alternative solution which enables a less complicated interface for the user is to provide current setting using a setting component, such as a resistor, outside the driver circuit. This resistor can for example be placed on a PCB which provides the interface between the driver circuit and the LED terminals, or the resistor can be integrated as part of a connection cable or connector unit. The value of the resistance is detected for subsequent control of the output of the driver circuit.
The value of the current setting resistor (or other component) influences the behavior of the driver circuit, which can then be used to configure its output accordingly, so that the output current is determined by the resistance value. Once the current has been set, the voltage delivered by the driver circuit will vary depending on the load presented to it (since the LEDs are current driven), but the driver circuit will maintain this voltage within the operating window.
A lighting module of this type is referred to as an analog module, and there is an analog interface, with the lighting module having a passive component with a value which indicates its power requirement. The average LED current is controlled and the LED current is maintained continuously. The driver circuit is for example based on a switched mode power converter architecture.
This known system does not allow the end user to change the current (and light output flux) of the lighting module. If a different current is needed, the setting resistor needs to be modified. Typically, the current setting resistor of the module cannot be changed by the customer.
When a customer uses lighting modules to build luminaires, there is often a need to optimize the luminaire to their preference, without being restricted to a fixed light output, temperature or power. For instance, an optical design may require less light output from the module. Alternatively, because a heat sink has been miniaturized, the module may run at too high temperature based on the default setting of the current setting resistor, and a reduced power is needed.
Hence, there is a need for the customer to be able to flexibly set the output current. One known solution is for the customer to apply a suitable current setting resistor into the driver. The driver then uses this component to define the output current.
An alternative to placing a setting resistor in the driver is to have a remotely settable drive current, which involves wireless communication with the driver to program the driver. The drive current is then set by the driver and no additional components in the lighting module are required.
The disadvantage of this approach is that the portfolio of drivers needs to be upgraded. This portfolio consists of many driver types (fixed output, dimming, DALI dimming, different housings, different power).
This means the implementation of the improved system will be slow and costly.